The particularity of certain medicines will also put forward higher requirements for the protection design of spray drying equipment. For materials dissolved in organic solvents, the entire system must meet the explosion-proof requirements when drying. At the same time, the explosion-proof type must be selected when designing accessories such as motors, instruments, and control valves. In addition, in order to prevent the solvent and air from mixing into explosive gas, the system adopts a closed circulation system, and the carrier should use inert gas, such as nitrogen. In addition, the drying of some easy-to-oxidize materials also requires a closed circulation system with nitrogen as the carrier.
Spray-dried products are fine particles, which are easy to form dust. In order to meet the requirements of environmental protection, it is not enough to use the conventional cyclone separator to separate products and purify the tail gas. A bag filter can also be used to purify, so that the dust content of the tail gas is less than 50 mg/cubic nanometer gas to reach the standard. ; Or use a wet scrubber to reduce the dust content of the exhaust gas to 15-35 mg/cubic nanometer gas. When the mesh belt dryer uses nitrogen as the carrier, the system should be airtight, and the exhaust port should be led to the outdoors.
Improving heat utilization is a top priority
The temperature of the hot air inlet is 250℃～500℃ in parallel operation and 200℃～300℃ in countercurrent operation. The outlet temperature after atomization and drying is generally controlled at 60℃～100℃, and its heat utilization rate is low. The disadvantages of spray drying.
At present, the thermal efficiency of domestic industrial-scale spray dryers is generally 30% to 50%. Foreign spray dryers with waste heat recovery can achieve a thermal efficiency of 70%, but the equipment is only economically meaningful when the production capacity is greater than 100 kg (water)/hour. However, when a nitrogen carrier and an organic solvent are used, a closed circulation system is adopted to allow the nitrogen to be recycled and the solvent to be condensed, which can effectively reduce the production cost.
But in general, the cost issue during the use of spray drying requires further research by equipment design and manufacturers to find better countermeasures to reduce costs.
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